Retinal Oxygen Delivery and Metabolism Response to Hyperoxia During Bilateral Common Carotid Artery Occlusion in Rats

Abstract

Purpose The purpose of the current study was to test the hypothesis that responses of total retinal blood flow (TRBF), inner retinal oxygen delivery (DO 2 ), metabolism (MO 2 ), and extraction fraction (OEF) to hyperoxia are higher after minutes of bilateral common carotid artery occlusion (BCCAO) as compared to days of BCCAO. Methods Twenty-eight rats were subjected to BCCAO for 30 minutes ( n = 12), 1 day ( n = 8), or 3 days ( n = 8). Eight of the 12 rats were also evaluated at baseline, prior to BCCAO. During room air breathing (RA) and 100% O 2 inspiration (hyperoxia), blood flow and phosphorescence lifetime imaging were performed to measure TRBF and vascular O 2 contents, respectively. DO 2 , MO 2 , and OEF were calculated from these measurements. Results After 30 minutes or 3 days of BCCAO, TRBF did not differ between RA and hyperoxia conditions ( P ≥ 0.14) but decreased under hyperoxia after 1 day ( P = 0.01). Compared to RA, DO 2 and MO 2 were increased under hyperoxia after 30 minutes of BCCAO ( P ≤ 0.02). Additionally, MO 2 was decreased under hyperoxia after 1 day of BCCAO ( P = 0.04). OEF was decreased under hyperoxia compared to RA ( P < 0.001). Under hyperoxia, TRBF and DO 2 were reduced after all BCCAO durations compared to baseline ( P ≤ 0.04), whereas MO 2 did not differ from baseline after 30 minutes of BCCAO ( P = 1.00). Conclusions The findings indicate that hyperoxia introduced minutes after ischemia can reduce DO 2 impairments and potentially return MO 2 to approximately normal values. This information contributes to the knowledge of the effect of supplemental oxygen intervention on TRBF, DO 2 , MO 2 , and OEF outcomes after variable durations of ischemia.